This application is for an ancillary study to determine the cognitive effects of homocysteine Iowering, as an additional outcome in an ongoing, randomized, controlled, double-blind clinical trial in renal transplant recipients (RTRs). Elevated plasma homocysteine levels are associated with diminished cognitive function in the general population, and significantly increase the risk of vascular disease, cerebrovascular disease, stroke and dementia. Hyperhomocysteinemia is a pervasive feature of chronic renal insufficiency, even after a successful transplant; however, unlike in other types of chronic renal insufficiency, homocysteine levels can be lowered in RTRs by high doses of B-vitamins. The parent trial (FAVORIT - NIH NIDDK UO1 DK61700-01) is designed to determine the effect of lowering plasma total homocysteine levels on atherosclerotic cardiovascular disease outcomes in chronic, stable RTRs. The FAVORIT trial aims to randomize 4000 RTRs with a stable functioning renal graft of > six months to a treatment or placebo group, and to follow them for 4 years or until the occurrence of a cardiovascular event or death. Treatment consists of a standard multivitamin with additional high dose folic acid, vitamin B12 and vitamin B6 and placebo consists of a multivitamin devoid of these vitamins. This application specifically aims to: (1) determine the cognitive effect of homocysteine lowering under this treatment regime; and (2), characterize cognitive function in relation to homocysteine and other risk factors for vascular disease in this high-risk, non-demented population. To do so we will measure cognitive outcomes in 1000 participants in the FAVORIT trial, at randomization and after a 3-4 year follow up. The outcome of this application may be highly significant in improving health care for RTRs and other groups with chronic renal insufficiency. Our long-term goal is to identify risk factors for cognitive impairment that can be modified through nutritional intervention or dietary supplementation in order to reduce the incidence of cognitive decline and dementia in elderly and other vulnerable populations. Demonstrating the cognitive benefits of lowering homocysteine may pave the way to nutritional modification of cognitive decline in RTRs and other high-risk groups and even in the general population.